1. Field of the Invention
The present invention relates to an image processing apparatus that corrects a hue and a saturation in a video signal, and an image processing method thereof.
2. Description of Related Art
An apparatus for correcting a hue and a saturation in a video signal of a moving picture in real time is generally mounted on a video apparatus such as a television receiver and a television camera for the purpose of a color adjustment or the like.
Conventionally, as an apparatus for correcting a hue of a video signal, there has existed one in which two color-difference signals are color-difference converted in a color-difference signal conversion matrix circuit respectively, these two color-difference converted signals are subjected to slicing respectively, and a color region to be corrected is extracted by taking a minimum value of the two sliced outputs (for example, refer to Japanese Laid-Open Patent Application No. H11-308628).
FIG. 8 is a block diagram showing a configuration example of a color signal extracting circuit of the above-mentioned hue correcting apparatus. In a color-difference signal Cb (=B−Y) and a color-difference signal Cr (=R−Y) which are input to this color signal extracting circuit, the color-difference signal Cb is supplied to variable gain amplifiers 51 and 52, respectively and the color-difference signal Cr is supplied to variable gain amplifiers 53 and 54, respectively. Output of the variable gain amplifier 51 and output of the variable gain amplifier 53 are added in an adder 55, and output of the variable gain amplifier 52 and output of the variable gain amplifier 54 are added in an adder 56.
A color-difference signal conversion matrix circuit 50 is configured with these variable gain amplifiers 51 to 54 and the adders 55 and 56, and a color-difference signal Cb′ which is color-difference converted is outputted from the adder 55, and a color-difference signal Cr′ which is color-difference converted is outputted from the adder 56.
These color-difference signal Cb′ and color-difference signal Cr′ are inputted to maximum input extracting circuits 57 and 58, respectively. In addition to these color-difference signal Cb′ and color-difference signal Cr′, coefficient signals having predetermined values are also inputted to the maximum input extracting circuits 57 and 58, respectively. The maximum input extracting circuits 57 and 58 are such circuits that extract a signal having a maximum value out of the respective two input signals, and function as circuits for slicing the color-difference signal Cb′ and the color-difference signal Cr′.
After the inputted coefficient signal to the maximum input extracting circuit 57 is subtracted from the output signal of the maximum input extracting circuit 57 in a subtracter 59, the resultant output signal of the maximum input extracting circuit 57 is inputted to a minimum input extracting circuit 61. Also, after the input coefficient signal to the maximum input extracting circuit 58 is subtracted from the output signal of the maximum input extracting circuit 58 in a subtracter 60, the resultant output signal of the maximum input extracting circuit 58 is input to the minimum value input extracting circuit 61.
The minimum input extracting circuit 61 is a circuit for extracting a signal having a minimum value out of the two input signals. An output signal of this minimum input extracting circuit 61 is an extracted color signal in which a color region to be corrected is extracted.
FIG. 9 is a diagram illustrating the color region extracted in the color signal extracting circuit of FIG. 8 on a color-difference plane with the color-difference signal Cb and the color-difference signal Cr indicated in the x axis and the y axis, respectively. By adjusting the gains of the variable gain amplifiers 51 to 54, a region A11 interposed between a half line b1 whose angle with respect to the x axis is θ1 and a half line b2 whose angle with respect to the x axis is θ2 is extracted as the color region to be corrected. A half line bm whose angle with respect to the x axis is θm is a point where the extracted color signal becomes maximum.
FIG. 10 is a diagram in which the extracted color signal output from the minimum input extracting circuit 61 is plotted three-dimensionally with respect to the color region shown in FIG. 9 (a diagram with the extracted color signal indicated in the Z axis). The extracted color signal becomes larger as a distance from an origin (a point where both the Cb and Cr are zero) on the color-difference plane becomes larger (that is, the saturation becomes higher), but in an angle direction (hue direction) on the color difference plane, the same curved lines are drawn regardless of the saturation.